Cigarettes currently cause 400,000 deaths a year in the United States. If we get all tobacco smokers to switch from regular cigarettes to electronic cigarettes, we would eventually reduce the US death toll from more than 400,000 a year to less than 4,000, maybe as low as 400.

If users stick to popular brands and use e-cigarettes sensibly I would say that the risk is negligible and compared with smoking, there is no contest. They are at least a 100 times less hazardous than cigarettes and they do not expose users to tar and carbon monoxide in the doses received.